Method of welding stainless steel



Patented May 19, 1953 METHOD OF WELDING STAINLESS STEEL Prentiss S. Viles, Baytown, Tex., assignor, by

mesne assignments, to Standard Oil Development Company, Elizabeth, N. J., a corporation of Delaware No Drawing. Application October 23, 1950, Serial No. 191,725

6 Claims. 1

The present invention is directed towards a method for welding ferrous alloys comprising substantially chromium, iron and nickel and referred to in the trade as stainless steels. More specifically the invention is directed toward the prevention of corrision due to welding of stainless steels which frequently manifests itself as an after effect when the welded stainless steels are employed.

This application is a continuation-in-part of Serial No. 716,669, now abandoned, filed December 16, 1946, for Prentiss S. Viles and entitled "Method for Welding Stainless Steel.

. The chromium nickel stainless steels are those containing nickel and chromium plus other ele-.- ments to a. lesser degree. These chromium nickel stainless steels are known a the austenitic chromium-nickel stainless steels, the nickel being added in sufficient amount to make the steels austenitic and nonmagnetic with improved ductility and conductiveness over the straight chrov mium steels.

These austenitic steels are outstanding in their resistance to corrosion and oxidation. 7 Because of their excellent physical properties both at low and elevated temperatures they find wide application in the food, pulp, paper, textile, dye, chemical, oil refining and other related industries. The severe corrosion encounteredin the use of these alloys, however, introduces many perplexingproblems and many uses will demand a selection among the various typesof steel available.

The corrosion characteristics of the steel are affected not only by the media in contact with the structural material but by the treatment the steel .is given in its fabrication into structural shapes and facilities. In fabricating containers, pipes .and various structural shapes and equipment it is necessary to employ welding. During the welding operation the stainless steel may be subjected to temperatures between 800 and 1600 F. whether the welding be accomplished by the oxy-acetylene, atomic hydrogen, or by the electric are methods. When the austenitic chromium nickel steels are subjected to temperatures between 800 and 1600 F. as occurs during welding, a structural change is effected in the steels. The carbon migrates out from the solid solution and combines with the chromium to form chromium carbides along the grain boundaries. This effect is known as carbide precipitation and this action impoverishes the chromium content adjacent to the grain boundaries; this increases the susceptibility to corrosion attack and leads to F what is generally referred to as intergranular corrosion at the grain boundaries.

The precipitation of carbide is affected by a" number of factors among which is the time the material is held within the critical temperaturerange. The longer the heat treatment the more. carbides precipitate and as the temperature approaches 1200 F. the more undesirable will be the structural change in the steel. It follows that the higher carbon content steels are more susceptible to carburization since there is more carbon available to combine with the chromium.

The problem of carbide precipitation and corrosion by intergranular attack has been solved in the industry by subjecting the welded metal to a heat treatment. The heat treatment involves heating the metal to a temperature between 1900 and 2000 F. for a sufficient time to bides forming again in passing through the critical temperature region.

Another method of suppressing the formation of chromium carbides in welding involves addition of several of the rare metals such as columbium and the like to the metals to act as stabilizers. These materials combine with the carbon and preventv or retard the formation of objectionable chromium carbides and thus reduce the tendency to intergranular corrosion.

The prior art methods in overcoming the formation of chromium carbides in the welding of stainless steels is expensive in that furnaces for the heat treatment must be provided which may also contribute to the cost of the steel. Too.

even with the addition of stabilizer metals, carbide formation may be encountered.

It is, therefore, the main object of the present: invention to provide a method of welding aus-'-' teniticstainless steel alloys which will substantially reduce or prevent the precipitation of chromium carbides at the grain boundaries of the metal and thus'reduce the susceptibility of the welded material to intergranular corrosion.

In accordance with the present invention the precipitation of carbides during welding opera-#- tions with its attendant degradation in the quality of the steel is materially reduced or substantially eliminated by the employment of a retarding agent during the welding operation. The

Lesser quantities give Welds which show. evidence.

of carbide precipitation while larger. amounts may be impractical.

In order to illustrate the. efiectiyeness of the.

present invention, a number of welds were made employing 18-8 steel alloys. Adjacent boundaries of the bodies of the alloys were welded? together in accordance with conventional welding techniques. was employed. In the following welds a conventional. flux. was. employed. except, that amoun s ranging from 0.1%; to 2.51% by weight. of elementary sulfur was. incorporated in the flux and applied. to the regiomol" the; adjacentboundaries oi'metal'sbeingwelded; These; welded. strips were thentestedi ion intergranular corrosion. by the Straus. test. The S raus test" consists car-immersing the specimens in boiling" Straus. solution (3%" cupri'c sulate, sulfuricacid" and 87%. dis-- tilled. water). for 722; hours. and then bending the I specimen rec The Straus test is" a method for. determining the. extent of carbide. precipitation in. metals. and a description thereof may" be found. in. the Welding; Handbook, 1938- edition, American Wel'ding Society; N. Y. pages 5-33- 1:

The. following table shows the condition of the several welds, aftertesting formetal loss in the Straus test;.

Table Stra1Is Test-72 Hours I ll leightt I 1 erccn Metal Welded p sum Metal oondmanmter in Flux Loss; 180.

1 I Rerccnt c3931 0 1.97, Brokemgranulan cracks. Do i f 0.1 0. 01 D0.

0.25 0. 01 Fain. some v1sible cracks. 0:5 O. 01- Good, 110 c1"acl s'.. l. 0. 0:01 Do. 7: 0 0. 0]." 10.0.. 15.0 0.01; D0. 25. 0. 0. 85 D0.

'1 American Iron and. Steel Substitute.

' The. data presented in: the forcgoingtable. show that the employmentofsuliur in the weldingfiux during: welding operations efiectively inhibits less ofxmetalwhen the welding. specimen is subjected to. a boilingStraus? solution- The. data further showv thatzthe stressing of the tested specimen produce less detrimen-talv effect in. the metal welded in. the presence of flux containing 0.25% to by weight of elementary sulfur, than the weldcondncted in: the absence of elementary sulfun in amounts: up: to 0.25% by Weight.

131;,may, be; concluded from the. results of. the.

In the first weld a conventional flux burization. and. metal carbide formation; thus,

a 4 chromium carbide is never formed in the process and, therefore, there are no chromium lean areas in the alloy after welding, this allows the alloy to retain its original corrosion resistant characteristics.

The weldingduxes to which. the. sulfur. is. added are the welding fluxes commonly used? in weldin stainless steels. Usually these welding fluxes are composed of some compound of the silicates, oxides, hydroxides, halides, carbonates, etc. of magnesium, calcium,.sodium, potassium, lithium, and other alkalior alkaline earth metals along ,w th. small. amounts. of salts of titanium, manganes columbiurn, vanadium, etc.

The welding fluxes mentioned above may have elementary sulfur in an amount in the range from 0 25%-to 25 %-by"wei ght incorporated therein and then applied either to the Welding rod or to the region. being welded. It is contemplated and may be preferred that the welding flux containing eleme tary su fu y b a pli a a c atin to lding, rods n. a-w sht rat o of welding flux. coating. on. the weldin rod in t i ee rom. to. 1:4 parts by weight.

The welding rods ermp'loyecl in the" practice of" the present invention may have a compos substantially the same as the stainless steel being welded. v It may be preferred; under some condi i' tions, however, that the welding rods contain I higher proportions of nickel and/or chromium than the alloy being wel'ded. Foriexampl e, whenv welding -8 steel; itmay be desirable to, use; 18:33 weld-ingrods. coated witha we l ding 'flux'in accprd? ance with the presentirnzention" or. use 19 -9; or 223-420" welding rods. A welding rod? of 18-8. or 19-9 stainless steel' having a coating of 1- part by weight. ofweldingflux of the type illustrated to 25 parts by weight of" weldingrod givesquitesatisfactory results in; the present invention.

When employing a flame-in the welding-operation the gases may be acetylene'or the liquefied petroleum gases, such as propane; butanes; butylenes, propylene, mixtures thereof, and the-like;

While the ox-y-acetylene torch" may" be used in the welding operation, the invention is equally applicable to electrical arc" welding'techniquesince most steels and alloys of. the type. menti'oned a bove contain carbon which. allows the formationof carbidesin the welding operation The invention is also applicable to welding using. atomic hydrogen'as'a source of heat.

The nature and objects or the present invention having been fully described and illustrated; what I Wish to; claim as, new and useful and to secure 'by'Letters Patent is z y 1-. A. met od of we dina ch ivme-nickelfsta m less steel which includes the steps of applying a. mixture-of a; conventional welding flux contain-l ing elementary sulfur in an amount in the range between-025% and'25% by weight, be as @5 5 cent boundaries of bodies. ofsaidsteel and weld"- mg said adjacent boundaries in the presence, of said'mixture. 'l '7 2. A method in accordance with claim 1 in which the steel isiwelded by applyingfan electric arc to the adjacent boundaries of bod 9f" sgid' steel.

a. A me hod n a rdance with claim 1 m h ch he ste l is lded by applyin an, we; acetylene flame to, the adjacentboundariesfor bodies ofsaid'steel". '7

4. A method in accordance with claim 1 in which the steel is welded by' ease was: rbon nam to the adjacent boundaries-bitches ofsaid'steel.

5. A method of Welding a chrome nickel stainless steel which includes the steps of forming a mixture of a conventional Welding flux and e1ementary sulfur, said mixture containing between 5% 1 2 by Weight of elementary sulfur, applying said mixture to tWo adjacent boundaries of bodies of said steel, and Welding said adjacent boundaries in the presence of said mixture.

6. A method in accordance with claim 5 in which the steel is welded by applying an oxyacetylene flame to the adjacent boundaries of bodies of said steel.

PRENTISS S. VILES.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,720,039 Green July 9, 1929 2,141,9 9 Moritz Dec. 27, 1938 Number Franks.

McGraw-Hill Book Co., New York, N. Y.

in Div. 3.)

Name Date Jones Feb. 18, 1941 Goodford Sept. 21, 1943 Landis et a1. Apr. 26, 1949 Landis Apr. 26, 1949 Lobosco June 21, 1949 FOREIGN PATENTS Country Date Great Britain Jan. 20, 1910 Great Britain June 17, 1937 Great Britain Nov. 27, 1941 OTHER REFERENCES Alloys of Iron and Chromium, by Kinsel and Vol. 2, Pub. by

( Copy p. 181 (103, Weld). 

1. A METHOD OF WELDING A CHROME-NICKEL STAINLESS STEEL WHICH INCLUDES THE STEPS OF APPLYING A MIXTURE OF A CONVENTIONAL WELDING FLUX CONTAINING ELEMENTARY SULFUR IN AN AMOUNT IN THE RANGE BETWEEN 0.25% AND 25% BY WEIGHT, TO TWO ADJACENT BOUNDARIES OF BODIES OF SAID STEEL AND WELDING SAID ADJACENT BOUNDARIES IN THE PRESENCE OF SAID MIXTURE. 